Light-weight RRC connection setup in multi-RAT network

ABSTRACT

The present disclosure generally relates to the field of Radio Resource Control (RRC). More specifically, the present disclosure relates to techniques of supporting and initiating RRC connection establishment in a wireless communication network. A method embodiment relates to supporting RRC connection establishment in a wireless communication network and comprises setting up context information during a first RRC connection establishment procedure to establish a first RRC connection towards a radio access network element (200) of the wireless communication network implementing a first Radio Access Technology (RAT). The context information is associated with a wireless communication device (100) of the wireless communication network and is usable for a second RRC connection establishment procedure to establish a second RRC connection towards a radio access network element of the wireless communication network implementing a second RAT.

TECHNICAL FIELD

The present disclosure generally relates to the field of Radio ResourceControl (RRC). More specifically, the present disclosure relates totechniques of supporting and initiating RRC connection establishment ina wireless communication network.

BACKGROUND

Radio Resource Control (RRC) is a signaling protocol which uses lowerlayers for segmentation and reliable in-order delivery of signalingmessages. RRC is suitable for messages of any size requiring reliabledelivery such as user equipment (UE) configuration. In Long TermEvolution (LTE) and LTE-advanced (LTE-a), RRC is involved in theNon-Access Stratum (NAS) message exchange between a UE and a MobilityManagement Entity (MME) as well as provide various control-planefunctions both on the UE and the evolved NodeB (eNodeB or, in short,eNB).

These control-plane functions include, on the eNB side, connectionmanagement, radio resource management, measurement configuration andmobility control, service management and security, system informationbroadcast and idle mode mobility. On the UE side, these control-planefunctions include idle mode mobility, for example. To be more specific,in connection management RRC may play a role in RRC connectionestablishment, maintenance and release, radio bearer connectionestablishment, maintenance and release, and multi-cell and multi-nodeconfigurations. In radio resource management, RRC may be involved inconfiguration of radio resources for RRC connection and configuration oflower layers and in radio configuration control including e.g.,assignment and/or modification of Automatic Repeat Request (ARQ)configuration, Hybrid Automatic Repeat Request (HARQ) configuration, andDiscontinuous Reception (DRX) configuration. Still further, inmeasurement configuration and mobility control, RRC may be used in UEmeasurement reporting and control of the reporting and mobilityfunctions (intra- and/or inter-frequency handover, and inter-RadioAccess Technology (inter-RAT) handover). In service management andsecurity, RRC may be involved in Multimedia Broadcast Multicast Service(MBMS) services, Quality of Service (QoS) management functions andAccess Stratum (AS) security, and, in system information broadcast, RRCmay be involved in Non-Access Stratum (NAS) (on idle mode mobilitymanagement and service setup) as well as AS (on data transfer and RRM).In idle mode mobility, RRC may be used in paging, cell reselection andsystem selection.

Typically, when a new Radio Access Technology (RAT) is standardized,this is done by also introducing a separate Core Network catering forthat RAT and 3GPP introduces mechanisms to move from one RAT to anotherRAT with minimal service interruption via the Core Network. Hence, inany case, moving from one RAT to another RAT means establishing a RRCconnection towards the target RAT and removing the RRC connection fromthe source RAT, and because those RRC connections terminate in differentlogical nodes anchoring in different Core Networks (i.e., are completelyseparate UE connections), there is no possibility of synergy betweenthem. This also implies a very high amount of signalling between thesource and the target RAT, and higher risks of call drops.

Thus, when a UE moves from one RAT to another RAT, the UE needs torelease the RRC connection in the source RAT and establish a new RRCconnection in the second RAT. The RRC connection procedure is identicalto the procedure happening when a UE initially connects to the secondRAT. This procedure is quite intense from the control signaling loadpoint of view, and it also adds a delay.

SUMMARY

Accordingly, there is a need for an improved Radio Resource Control(RRC) connection establishment technique in a wireless communicationnetwork.

According to a first aspect, a method of supporting Radio ResourceControl (RRC) connection establishment in a wireless communicationnetwork is provided. The method comprises setting up context informationduring a first RRC connection establishment procedure. The first RRCconnection establishment procedure is to establish a first RRCconnection towards a radio access network element of the wirelesscommunication network implementing a first Radio Access Technology(RAT). The context information is associated with a wirelesscommunication device of the wireless communication network. The contextinformation is usable for a second RRC connection establishmentprocedure to establish a second RRC connection towards a radio accessnetwork element of the wireless communication network implementing asecond RAT.

RAT, Radio Access Network Element

In this way, the context information set up during the first RRCestablishment procedure can be reused for the second RRC connectionestablishment procedure. As a consequence, the second RRC connectionestablishment procedure can be simplified.

The context information may be regarded as information in a radio accessnetwork element associated with an active wireless communication device.The information may contain the necessary information required tomaintain the radio access network services towards the active wirelesscommunication device. For example, at least one of state information ofthe wireless communication device, security information, and capabilityinformation of the wireless communication device may be included in thecontext information. Establishment of the context information may becompleted in the radio access network element when the transition toactive state for the wireless communication device is completed.

The term Radio Access Technology (RAT) may be understood as theunderlying physical connection mechanism for a radio based communicationnetwork. The radio access network element may comprise or be configuredas a base station of a radio access network.

The step of preparing may comprise receiving, by the radio accessnetwork element implementing the first RAT, the context information orinformation needed for setting up the context information.

The radio access network element implementing the first RAT maycorrespond to or may be different from the radio access network elementimplementing the second RAT.

If the radio access network element implementing the first RAT isdifferent from the radio access network element implementing the secondRAT, the method may comprise providing, by the radio access networkelement implementing the first RAT, the context information orinformation needed for setting up the context information to the radioaccess network element implementing the second RAT. In this way, theradio access network element implementing the second RAT can be informedabout the context information or the information needed for setting upthe context information by the radio access network element implementingthe first RAT.

In one or more embodiments, the method may comprise providing thewireless communication device with information related to theestablishment of the second RRC connection. In this way, the wirelesscommunication device can be information about the Information related tothe establishment of the second RRC connection.

The method may comprise providing the information related to theestablishment of the second RRC connection in a Downlink (DL) message ofthe first RRC connection establishment procedure. Alternatively oradditionally, the method may comprise providing the information relatedto the establishment of the second RRC connection via broadcast systeminformation.

The information related to the establishment of the second RRCconnection may comprise a cell identity of the cell associated with theradio access network element implementing the second RAT. Alternativelyor additionally, the information related to the establishment of thesecond RRC connection may comprise an identifier to be used whenaccessing the radio access network element implementing the second RAT.Alternatively or additionally, the information related to theestablishment of the second RRC connection may comprise accessinformation for accessing the radio access network element implementingthe second RAT. Alternatively or additionally, the information relatedto the establishment of the second RRC connection may compriseinformation about conditions or trigger events indicating when toconnect to the radio access network element implementing the second RAT.Alternatively or additionally, the information related to theestablishment of the second RRC connection may comprise securityre-activation information for the second RRC connection establishmentprocedure such as nextHopChainingCount for the second RRC connectionestablishment procedure.

According to a second aspect, a method of initiating Radio ResourceControl (RRC) connection establishment in a wireless communicationnetwork is provided. The method may comprise initiating, using contextinformation, a second RRC connection establishment procedure. The secondRRC connection establishment procedure is to establish a second RRCconnection towards a radio access network element of the wirelesscommunication network implementing a second Radio Access Technology(RAT). The context information is associated with a wirelesscommunication device of the wireless communication network. The contextinformation is set up during a first RRC connection establishmentprocedure. The first RRC connection establishment procedure is toestablish a first RRC connection towards a radio access network elementof the wireless communication network implementing a first RAT.

The step of initiating may comprise transmitting an RRC reestablishmentmessage.

The method may comprise providing the radio access network elementimplementing the second RAT with a previous identifier of the wirelesscommunication device. This previous identifier may be UE RRC contextidentifier informed by the former radio access network element (e.g.eNB)/RAT. The previous identifier of the wireless communication devicemay comprise at least one of Cell Radio Network Temporary Identifier(C-RNTI), a Physical Cell Identifier (PCI) and RAT category associatedwith the first RAT. Here, the term RAT category may correspond to theRAT type, e.g. LTE or a new radio access technology, and/or therelease/capability of the first RAT.

According to a third aspect, a method of initiating Radio ResourceControl (RRC) connection establishment in a wireless communicationnetwork is provided. The method comprises setting up context informationduring a first RRC connection establishment procedure. The first RRCconnection establishment procedure is to establish a first RRCconnection towards a radio access network element of the wirelesscommunication network implementing a first Radio Access Technology(RAT). The context information is associated with a wirelesscommunication device of the wireless communication network. The contextinformation is usable for a second RRC connection establishmentprocedure. The second RRC connection establishment procedure is toestablish a second RRC connection towards a radio access network elementof the wireless communication network implementing a second RAT. Themethod further comprises initiating, using the context information, thesecond RRC connection establishment procedure to establish the RRCconnection towards the radio access network element of the wirelesscommunication network implementing the second RAT.

The method may comprise in parallel establishing the first RRCconnection towards the radio access network element implementing thefirst RAT and the second RRC connection towards the radio access networkelement implementing the second RAT.

For example, establishing the first RRC connection towards the radioaccess network element implementing the first RAT and the second RRCconnection towards the radio access network element implementing thesecond RAT in parallel may comprise establishing the first RRCconnection towards the radio access network element implementing thefirst RAT and the second RRC connection towards the radio access networkelement implementing the second RAT simultaneously. The first RRCconnection towards the radio access network element implementing thefirst RAT and the second RRC connection towards the radio access networkelement implementing to the second RAT may also be started at differenttimes but at least a portion of both may be established in parallel. Thefirst RRC connection towards the radio access network elementimplementing the first RAT and the second RRC connection towards theradio access network element implementing the second RAT may also bestarted sequentially.

The method may comprise establishing the second RRC connection towardsthe radio access network element implementing the second RAT by usingthe context information.

The method may comprise maintaining the first RRC connection towards theradio access network element implementing the first RAT and the secondRRC connection towards the radio access network element implementing thesecond RAT at the same time.

The method may comprise establishing the second RRC connection towardsthe radio access network element implementing the second RAT, if thefirst RRC connection towards the radio access network elementimplementing the first RAT is lost, e.g. released or failed. The termlost may include one or more or a Radio Link Failure (RLF) a Release orHandover failure or any other type of failure.

The method may comprise establishing the second RRC connection towardsthe radio access network element implementing the second RAT based on atleast one of a trigger event and a network command. The network commandmay be made or issued by the radio access network element implementingthe first RAT, for example.

The trigger event may comprise or be a Radio Link Failure (RLF) of thefirst RRC connection towards the radio access network elementimplementing the first RAT.

According to a fourth aspect, a computer program is provided. Thecomputer program comprises program code portions for causing the stepsof any one of the method aspects described herein to be performed, whenthe computer program is run on a computer system or on one or morecomputing devices. The computer program may be stored on acomputer-readable recording medium or may be downloadable as a signal.

According to a fifth aspect, a radio access network element forsupporting Radio Resource Control (RRC) connection establishment in awireless communication network is provided. The radio access networkelement comprises a set-up component. The set-up component is configuredto set up context information during a first RRC connectionestablishment procedure. The first RRC connection establishmentprocedure is to establish a first RRC connection towards a radio accessnetwork element of the wireless communication network implementing afirst Radio Access Technology (RAT). The context information isassociated with a wireless communication device of the wirelesscommunication network. The context information is usable for a secondRRC connection establishment procedure. The second RRC connectionestablishment procedure is to establish a second RRC connection towardsa radio access network element of the wireless communication networkimplementing a second RAT.

The radio access network element may be or comprise at least one of theradio access network element implementing the first RAT and the radioaccess network element implementing the second RAT.

The radio access network element may be configured to perform the methodof any of the method steps described herein with respect to the firstaspect. The radio access network element may comprise or be configuredas or be part of a radio base station, a radio network controller (RNC),a nodeB, an eNodeB or a 5G base station.

According to a sixth aspect, a wireless communication device forinitiating Radio Resource Control (RRC) connection establishment in awireless communication network is provided. The wireless communicationdevice comprises an initiating component. The initiating component isconfigured to initiate, using context information, a second RRCconnection establishment procedure to establish a second RRC connectiontowards a radio access network element of the wireless communicationnetwork implementing a second Radio Access Technology (RAT). The contextinformation is associated with a wireless communication device of thewireless communication network. The context information is set up duringa first RRC connection establishment procedure. The first RRC connectionestablishment procedure is to establish a first RRC connection towards aradio access network element of the wireless communication networkimplementing a first RAT.

The wireless communication device may be configured to perform themethod of any of the method steps described herein with respect to thesecond aspect.

According to a seventh aspect, a wireless communication system isprovided. The wireless communication system comprises the radio accessnetwork element as described herein and one or more wirelesscommunication devices such as user equipments (UEs). The wirelesscommunication system may be configured to perform the steps of any oneof the method aspects as described herein with respect to the thirdaspect.

In general, the steps of any one of the method aspects described hereinmay equally be performed in one or more suitable components, devices orunits, e.g. in suitable components of the radio access network element,the wireless communication device and/or the wireless communicationsystem.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following, the present disclosure will be further described withreference to exemplary embodiments illustrated in the Figures, in which:

FIG. 1 is a schematic illustration of an embodiment of a systemcomprising a device embodiment of a wireless communication device and adevice embodiment of a radio access network element;

FIG. 2 is a flowchart illustrating a method embodiment performed in thesystem of FIG. 1;

FIG. 3 a flowchart of an LTE RRC connection setup and attach procedures;

FIG. 4 a flowchart of an RRC connection establishment for the “Attach”case in E-UTRAN;

FIG. 5 a possible implementation the embodiment of the system of FIG. 1;

FIG. 6 a flowchart illustrating a control signaling flow that may beused in the method of FIG. 2;

FIG. 7 is a block diagram schematically illustrating an embodiment of aradio access network element or a wireless communication device;

FIG. 8 is a block diagram schematically illustrating a furtherembodiment of a radio access network element; and

FIG. 9 is a block diagram schematically illustrating a furtherembodiment of a wireless communication device.

DETAILED DESCRIPTION

In the following description, for purposes of explanation and notlimitation, specific details are set forth, such as specific networktopologies including particular network nodes, in order to provide athorough understanding of the present disclosure. It will be apparent toone skilled in the art that the present disclosure may be practiced inother embodiments that depart from these specific details. For example,although the present disclosure is mainly described with reference toLong Term Evolution (LTE) as a specific example for a wirelesscommunication network, the present disclosure may be practiced in anynetwork to which mobile or stationary users using a corresponding userequipment (UE) may attach. For example, the present disclosure isapplicable to other cellular networks such as Global System for MobileCommunications (GSM) networks, Universal Mobile TelecommunicationsSystem (UMTS) networks, LTE-Advanced (LTE-A) networks, 5G networks, WiFinetworks or to Wireless Local Area Network (WLAN) or similar wirelessnetworks and a combination thereof.

Those skilled in the art will further appreciate that functionsexplained herein below may be implemented using individual hardwarecircuitry, using software functioning in conjunction with a programmedmicroprocessor or a processor of a general purpose computer, using anApplication Specific Integrated Circuit (ASIC) and/or using one or moreDigital Signal Processors (DSPs). It will also be appreciated that whenthe present disclosure is described as a method, the present disclosuremay also be embodied in a computer processor (e.g. embodied as one ofthe aforementioned types) and a memory coupled to the processor, whereinthe memory is encoded with or stores one or more programs to cause theprocessor to perform the methods disclosed herein when executed by theprocessor.

FIG. 1 shows an embodiment of a wireless communication system 10comprising an embodiment of a wireless communication device 100 and anembodiment of a radio access network element 200.

The wireless communication device 100 is adapted for initiating RadioResource Control (RRC) connection establishment in a wirelesscommunication network. The wireless communication device 100 may be,comprise or be part of a user equipment (UE) operable in accordance withLTE or LTE-A.

The wireless communication device 100 comprises an Initiating component120 and may further comprise a receiving component 140. The initiatingcomponent 120 is configured to initiate, using context information, anRRC connection establishment. The context information is associated withthe wireless communication device 100 of the wireless communicationnetwork. The context information is set up during a first RRC connectionestablishment procedure. The first RRC connection establishmentprocedure is to establish a first RRC connection towards a radio accessnetwork element, e.g. radio access network element 200, of the wirelesscommunication network implementing a first Radio Access Technology(RAT). More particularly, the initiating component 120 is configured toinitiate, using the context information, a second RRC connectionestablishment procedure to establish a second RRC connection towards aradio access network element, e.g. radio access network element 200 oranother radio access network element, of the wireless communicationnetwork implementing a second RAT. The receiving component 140 may beconfigured to receive information, e.g. from the radio access networkelement 200.

The radio access network element 200 is adapted for supporting RadioResource Control (RRC) connection establishment in a wirelesscommunication network. The radio access network element 200 may be,comprise or be part of an eNodeB operable in accordance with LTE orLTE-A.

The radio access network element 200 comprises a set-up component 220and may further comprise a receiving component 240 and/or a providingcomponent 260. The set-up component 220 is configured to set up contextinformation during a first RRC connection establishment procedure. Thefirst RRC connection establishment procedure is to establish a first RRCconnection towards a radio access network element, e.g. radio accessnetwork element 200 or another radio access network element, of thewireless communication network implementing a first Radio AccessTechnology (RAT). The context information is associated with a wirelesscommunication device 100 of the wireless communication network. Thecontext information is usable for a second RRC connection establishmentprocedure. The second RRC connection establishment procedure is toestablish a second RRC connection towards a radio access networkelement, e.g. radio access network element 200 or another radio accessnetwork element, of the wireless communication network implementing asecond RAT. The receiving component 240 may be configured to receiveinformation, e.g. from wireless communication device 100. The providingcomponent 260 may be configured to provide information, e.g. to thewireless communication device 100.

The wireless communication device 100 and the radio access networkelement 200 will be further described below with respect to FIG. 2.

FIG. 2 shows a method embodiment which can be implemented in thewireless communication system 10 of FIG. 1. In more detail, the firststep S202 of FIG. 2 shows a method embodiment which can be implementedin the radio access network element 200 of FIG. 1 and the second stepS204 of FIG. 2 shows a method embodiment which can be implemented in thewireless communication device 100 of FIG. 1.

The method of FIG. 2 is for initiating Radio Resource Control (RRC)connection establishment in a wireless communication network.

In step S202, context information is set up during a first RRCconnection establishment procedure. The first RRC connectionestablishment procedure is to establish a first RRC connection towards aradio access network element, e.g. radio access network element 200 oranother radio access network element, of the wireless communicationnetwork implementing a first Radio Access Technology (RAT). The contextinformation is associated with a wireless communication device 100 ofthe wireless communication network. The context information is usablefor a second RRC connection establishment procedure. The second RRCconnection establishment procedure is to establish a second RRCconnection towards a radio access network element, e.g. radio accessnetwork element 200 or another radio access network element, of thewireless communication network implementing a second RAT. For example,the set-up component 220 is configured to set up the context informationduring the first RRC connection establishment procedure.

In step S204, the second RRC connection establishment procedure isinitiated using the context information. The second RRC connectionestablishment procedure is to establish the RRC connection towards theradio access network element, e.g. radio access network element 200 oranother radio access network element, of the wireless communicationnetwork implementing the second RAT. For example, the Initiatingcomponent 120 is configured to initiate, using the context information,the second RRC connection establishment procedure.

The present disclosure is described in the following mainly within thecontext of LTE. It should be understood that the problems and solutionsdescribed herein are equally applicable to wireless access networks anduser equipments (UEs) implementing other access technologies andstandards. Thus, LTE is used as an example technology where the proposedtechnique is suitable, and using LTE in the following therefore isuseful for understanding the technique described herein. Thus, in thefollowing, for sake of explanation rather than limitation, the radioaccess network element 200 will be referred to as eNB 200 to illustrate,by way of example, that the radio access network element 200 can beconfigured as a base station and that the technique proposed herein canbe used and implemented in LTE. Similarly, the wireless communicationdevice 100 will be referred to as UE 100 to illustrate, by way ofexample, that the technique proposed herein can be used and Implementedin LTE.

Similarly, the context information will be referred to as eNB UEcontext. The eNB UE context may be understood in the sense of 3GPP TS36.401 V12.2.0 (2015-03) as a block of information in an eNB associatedwith one active UE. The block of information may contain the necessaryinformation required to maintain the evolved Universal MobileTelecommunications System (UMTS) terrestrial radio access network(E-UTRAN) services towards the active UE. For example, one or more or UEstate information, security information, UE capability information andthe identities of the UE-associated logical S1-connection may beincluded in the eNB UE context. Establishment of the eNB UE context maybe considered completed when the transition to active state for a UE iscompleted or in target eNB after completion of handover to E-UTRAN. TheEvolved UMTS Universal Terrestrial Radio Access (E-UTRA) is the airinterface of 3GPP's Long Term Evolution (LTE) upgrade path for mobilenetworks. It is also referred to as the 3GPP work item on the LTE alsoknown as the Evolved Universal Terrestrial Radio Access (E-UTRA) inearly drafts of the 3GPP LTE specification. E-UTRAN is the combinationof E-UTRA, UEs and eNBs.

Further exemplary details regarding UE 100, eNB 200, the system 10comprising UE 100 and eNB 200, and the methods performed therein aredescribed below with respect to FIGS. 5 to 9. Before these details areexplained, the general concept of RRC connection establishment isexplained with respect to FIGS. 3 and 4.

As shown in FIGS. 3 and 4, for RRC connection establishment between UE 1and eNB 2, UE 1 first sends a random access preamble to eNB 2 (see stepS402). In step S404, eNB 2 responds to UE 1 with a random accesspreamble response. In step S406, UE 1 sends a RRC connection requestmessage to eNB 2. The eNB 2 responds either with a RRC connection setupreject message as shown in FIG. 3 or with a RRC connection setup confirmmessage as shown in FIG. 4 (see step S408). In the latter case, UE 1responds with a RRC connection setup complete message to indicate thatthe RRC connection is established (step S410). In step S412, eNB 2transmits an initial UE message to MME 3.

When evolving the current LTE system to add a new radio accesstechnology (which is called NX in the following as a place holder), onearrives at multiple Radio Access Technologies (RATs). In this case, onecould have only one UE connection towards the Core Network (CN) and thatconnection may contain both RAT components, i.e. the existing RAT(E-UTRA) and the new RAT (NX). The CN could be common or be mapped toone or more common slices and/or instances of CN functions or entities.That is, when evolving LTE with Nx in 5G, the assumption it can beassumed to have only one connection from the radio access network (RAN)to the core network (CN). Today, when a UE moves from one RAT to another(e.g. from 3G/GSM, WDCMA to 4G/LTE) the UE has to release the RRCconnection in the source RAT and to establish a new RRC connection inthe target RAT. This is a long and complex procedure with a risk forfailure. Further, using the RRC connection procedure described withrespect to FIGS. 3 and 4 for both RATs leads to a high signaling load.

By means of the methods described above with respect to FIG. 2, thepossibility is enabled for UE 100 which has or is establishing a firstRRC connection, e.g. an RRC connection in E-UTRAN or NX, to establish asecond RRC connection towards a second RAT (e.g. in NX or E-UTRAN) whilemaintaining a single and already existing connection to the CN.Furthermore, by the UE context set up earlier, the RRC establishment tothe second RAT is enhanced so that the RRC connection may be establishedin shorter time. Further, the signaling procedure may be simplified forthe second RRC establishment by using the UE context known at thenetwork side. E-UTRAN and NX may be tightly integrated to enhance userperformance, for instance. For example, UE 100 may be connected to oneCore Network by one evolved S1 association, supporting both radio accesstechnologies. In this way, UE 100 may be enabled to establishsimultaneous RRC connections towards two different RATs, one towardsE-UTRAN and another towards NX, while keeping a common anchoring andcontrol point on the NW side.

In consequence, UE 100 can be adapted to maintain two RRC connections atthe same time, each one via a different RAT. Connection establishmentvia the second RAT is facilitated by re-using information used for theconnection via the first RAT and/or already being communicated via thefirst RAT connection. Therefore, the signaling load on the air interfaceof the second RAT and the processing capacity in UE 100 are low, and thechange in the connections between the RANs and UE 100 is transparent tothe CN.

The connection via the first RAT may be simultaneously established withrespect to the connection via the second RAT or may have been terminatedbefore establishment of connection via the second RAT, e.g. due to radiolink failure (RLF). The connection via the first RAT and the connectionvia the second RAT may use the same radio bearer or may use a differentradio bearer (e.g. one uses a default bearer). The connection betweenthe RAN and the CN may also use the same bearer (for example, as adefault scenario) or may use separate bearers. The base station (BS) forthe connection via the first RAT may be the same as or different fromthe BS for the connection via the second RAT (in this case, there iscommunication between BSs regarding UE context information). In thefirst scenario, UE 100 can connect to eNB 200 for connection via thefirst and the second RAT. In the second scenario, UE 100 may connect toeNB 200 for connection via the first RAT and may connect to another eNBfor connection via the second RAT.

To explain further, in a first case, there can be separate RRC entitlesfor different RATs in one eNB, e.g. In eNB 200. For example, UE 100separately sends RRC message(s) to different RATs to set up the RRCconnection, e.g. one RRC connection (set up) request to first RAT andRRC connection re-establishment request to second RAT. Then, the UEcontext may be created and transferred for the second RAT's RRC. In casethe eNBs implementing the first RAT and second RAT are different, thebenefit is that once UE context related information has been sent to oneRAT, the UE context related information does not have to be sent toanother RAT.

Alternatively, in a second case, there can be a common RRC layer fordifferent RATs, e.g. It can reside in a single (master) node. In otherwords, there may be a common RRC (which may reside in a single node ifthere are multiple nodes) and a common RRC state machine. Then, there asingle RRC layer and RRC connection for both RATs may be set uptogether. In that case, only one physical (PHY) link (the first one) maybe used for the set-up. In other words, RRC message exchange with thefirst RAT would be enough to set up the RRC connection with both RATs(without any need for RRC connection re-establishment message exchange).In a first variant of the first case, it is conceivable that the UEcontext for the second RAT can be created by the first RAT's RRC withoutinvolving the second RAT's RRC in the context set-up process initially.In a second variant of the first case UE context for the second RAT canbe created by the first and second RATs RRCs' involvement together. In athird variant of the first case, UE context for the second RAT can becreated by the second RAT's RRC, transparent to the first RAT's RRC.

The UE context can be created (set up) for the second RAT within the RRCof the first RAT. Alternatively, the UE context can be created (set up)for the second RAT within the RRC of the second RAT (based on theinformation needed for setting up the (UE) context).

In more detail, as illustrated in FIGS. 5 and 6, the following may beperformed by UE 100 and/or eNB 200. For illustration rather thanlimitation, a first RAT (RAT1) and a second RAT (RAT2) are supported bythe same eNB, i.e. eNB 200, in FIGS. 5 and 6. However, this is not to beunderstood as limiting. Rather, RAT1 and RAT2 may be supported bydifferent eNBs, e.g. RAT1 by eNB 200 and RAT2 by a different eNB.

Thus, the present disclosure is equally applicable independent ofwhether one BS implements both RATs or whether the two RATS areimplemented separately.

In step S602, UE 100 initiates the RRC connection establishmentprocedure to establish an RRC connection in the first RAT. This step mayalso be referred to as RRC connection setup. In other words, the RRCconnection establishment procedure may start by UE 100 initiating theRRC connection establishment procedure towards one of the RATs (E-UTRAor NX) by sending a random access preamble as shown in FIGS. 3 and 4.

In step S602, one connection via first RAT is established. The secondconnection via second RAT can be added later. Establishment of secondconnection can be triggered by an event like, for example, RLF of firstconnection or the NW may request the UE to establish the secondconnection via the second RAT, e.g. In case the UE is in coverage.

Before performing RRC connection establishment towards the second RAT,the following is performed. The BS of the first RAT is informed about UEcontext information (e.g. UE state information, security information, UEidentities, UE radio capabilities and the like). If there are two BSsfor the first RAT and the second RAT, the BS for the first RAT informsthe BS for the second RAT about this information.

To explain further, in the response to successfully finalize the RRCconnection establishment procedure in the first RAT (i.e., RRCconnection establishment procedure successfully ends with the sending ofthe response message), the network (NW), e.g. eNB 200, may indicate toUE 100 if, when accessing the second RAT, UE 100 should use a secondprocedure to establish the connection in the second RAT or the sameprocedure as used for the first RAT. The second procedure may be asignaling load reduced, called light-weight, RRC connection setup asillustrated in step S606. This indication may be provided in a downlinkmessage e.g., during the RRC connection procedure. The network mayprovide different information to UE 100 such as the conditions by whichUE 100 will connect to the second RAT, and/or how to access the secondRAT. For example, the NW may further provide UE 100 with asconfiguration parameters, IDs, bearer IDs, and other relevantinformation to access the second RAT, e.g. PHY/MAC/RRC layer parametersand other variables (access information may include second RAT C-RNTI,second RAT security algorithm identifiers, dedicated second RAT RandomAccess Channel (RACH) preamble or resources for access second RAT,second RAT SIBs, second RAT spectrum etc.).

To explain further, when informing UE 100, the BS of first RAT or secondRAT may inform UE 100 about the cell identify of the cell associatedwith second RAT, which can be either explicitly communicated (sameBS/different BSs) or can be derived from other information (same BS).This information can be conveyed in dedicated signaling or via systeminformation broadcast. Optionally, UE identifier to be used for secondRAT can be provided, so that the BS can associate already available UEcontext information with UE 100. The UE identifier can be sent to UE 100prior to the connection set-up via the second RAT and/or UE 100 caninclude its previous UE identifier when the UE 100 sends the connectionset-up message to the BS for the second RAT. Either measure may help theBS for second RAT to retrieve information on UE 100. This informationmay be conveyed prior to initiation of the connection establishment,e.g. In the RRC reconfiguration message (step S604) or any earlier RRCmessage or system information block (SIB).

As stated above, all the necessary information to access the second RATmay be provided during the RRC connection establishment process in a DLmessage, or at any time after successful completion of the RRCconnection establishment with the first RAT. For example, the networkcan provide a UE RRC context identifier in advance so that the UE cansend this identifier to the next eNB/RAT when it sends light-weight RRCconnection setup request. The network can also use this identifier tofind/fetch the UE context associated to the UE. The necessaryinformation (or parts of it) could also be distributed via systeminformation.

As mentioned above, establishment of the second connection can betriggered by a trigger event like RLF of first connection or a networkcommand. Conditions/trigger events when to connect via the second RATmay include an Indication that higher data rate desired, an indicationthat more reliability of connection is desired, an indication that RLFis detected on the first connection, and the like. To give an example,the network command may be made by the first RAT node (e.g., forsetting-up dual connectivity).

Regarding the RLF in LTE, when RLF happens, UE 100 first tries torecover. If UE 100 does not recover with another cell, UE 100 may go tothe RRC idle state. If UE 100 recovers with a cell of a second RAT, UEcontext may still stay in the LTE cell. Thus, if the first connection islost, the second connection can be established for seamless connectionto the network.

Returning to FIG. 6, UE 100 initiates a RRC connection establishmentprocedure to establish an RRC connection in the second RAT. When UE 100establishes the RRC connection towards the second RAT, UE 100 may startlight-weight RRC connection towards the second RAT (see step S606).Light-weight RRC connection towards the second RAT may be initiated ifthe NW configured UE 100 with it. In the exemplary illustration of FIG.6, UE 100 starts RRC connection re-establishment as the light-weight RRCconnection setup in step S606. Connection establishment from the UE tothe BS of the second RAT can be performed using the RRC reestablishmentmessage in LTE, for example. In the message the UE identifier or the UEidentifier and the cause (as in RRC connection re-establishment message)or the UE identifier, the cause and the context (capabilities and/orattributes) that were not sent and/or retrieved by the second RAT may beincluded. The UE identifier can be C-RTNI and previous cell ID. Toexplain further, light-weight RRC connection establishment of step S606may include one or more of the following messages: Light-weight RRCconnection setup request (from UE to NW), Light-weight RRC connectionsetup message (from NW to UE), and Light-weight RRC connection setupcomplete (from UE to NW). For example, light-weight RRC connectionestablishment of step S606 may include the complete message sequence ofLight-weight RRC connection setup request (from UE to NW), Light-weightRRC connection setup message (from NW to UE), and Light-weight RRCconnection setup complete (from UE to NW). There may be also one or moreprior messages that can include information to be used later forLight-weight RRC connection setup request.

The second RAT context may be created within the first RAT connectionsetup, without or with limited involvement of the second RAT (node).This enables context fetch of at least a part of the context related tothe second RAT (node) which is stored at the first RAT (node) until thesecond RAT connection is physically set up (due to security reasons orsimply to save memory, etc.). The UE identifier (e.g. C-RTNI and sourcecell ID) included in the light-weight RRC connection request message canhelp the second RAT (node) to fetch the (remaining) second RAT contextfrom the first RAT (node). That is, the UE context for second BS can beprepared when context for first BS is generated such that theestablishment of second connection is facilitated by already availableinformation.

There are several options of how UE 100 can determine whether it can usea light-weight procedure as illustrated in step S606 or not.

According to a first embodiment, the network may indicate if the UE 100can or should use this method to access the second RAT or if UE 100should use the same method as used for the RRC connection establishmentin the first RAT. This embodiment can be implemented in variousvariants, all of which can be suitably combined with each other.

According to a first variant, the NW may inform UE 100 during radioaccess in the second RAT if light-weight RRC connection establishment isenabled. According to a second variant, the second RAT may broadcast iflight-weight RRC connection establishment is allowed. According to athird variant, the network could also indicate whether light-weight RRCconnection establishment should be used when specifically accessingcertain nodes within the second RAT. Thus, the network could provide,for example, a list of network nodes in which UE 100 could access usingthe light-weight RRC connection establishment procedure. This means thatUE 100 would use the first method to access those nodes not listed bythe network. In a fourth variant, the network could indicate whetherthis second method should be used only when an RRC connection towardsone of the RATs is already or being established, or whether this secondmethod should be used until further notice i.e., until another DLmessage to disable this second method is sent by the network (e.g., inthe RRC Connection Release, RB reconfiguration), or until certainconditions are triggered (e.g., tracking area update, UE establishing aconnection in a different RAT e.g., UTRAN, security failure, etc.).

Alternatively to the methods above in which the network indicates howand if the UE 100 is allowed to access the second RAT, in a secondembodiment, the second procedure to establish an RRC connection towardsa second RAT may be mandated under certain conditions. In this case, UE100 would always use this method. For example, UE 100 may be mandated toalways access the second RAT using a second procedure e.g., alight-weight RRC connection procedure according to step S606 if UE 100had a RRC connection in the first RAT.

In one implementation, when UE 100 starts the RRC connectionestablishment in the second RAT, UE 100 may follow the procedureindicated by the network unless mandated by the standards.

The embodiments and variants mentioned above can be implemented inisolation or in conjunction with each other, e.g. they are allindependent and the use of one does not necessary exclude other.

Upon a successful complete of the light-weight RRC connection signaling,UE 100 can be configured with new radio bearers, e.g., by means of RRCconnection reconfiguration (see step S608). In addition, the UE context(e.g., UE state information, security information, UE identities, and UEradio access capabilities) related to the second RAT can be updated orcompleted following the light-weight RRC connection setup. If UE 100 haspreviously received nextHopChainingCount as defined in 3GPP TS 36.311,the step S608 might not be needed but RRC reconfiguration (thatconfigures not only signaling radio bearers but also data radio bearers)can be handled together with light-weight RRC connection setup messagefrom eNB to UE.

By way of the above, light-weight RRC connection setup to a secondnetwork in a multi-RAT setup is enabled.

In cases where the first RAT and the second RAT are not co-locatedwithin the same logical node (e.g., eNB 200), the first and the secondRAT may exchange control information between each other via an internalNW interface (e.g., X2 or S1) or OAM, in order to coordinatelight-weight RRC connection establishment. Interactions between RAN andCN (e.g. Evolved Packet Core (EPC)) 300, i.e. in AS and NAS, areexplained further in the following. It is assumed the EPC does not needto be aware that the UE is connected via two different RRC connectionsover the LTE and NX RATs. Whether there is a need for an exchange ofinformation between eNB 200 and MME of EPC 300 at establishment of thesecond RRC connection would depend on that second RRC connectioncorresponding to new radio access bearers or not (and in particular if adefault bearer is needed on the second RAT in case of separate bearers)or if any EPC-relevant information needs to be updated once UE 100 isconnected to the second RAT. There could be reasons to contact EPC 300e.g. to provide information used for charging purposes when the secondRAT is used, legal aspects like Lawful Intercept or Security relatedaspects inherent to the second RAT. In case of split bearers, the MMEwould not notice the establishment of a second RAT (similar to splitbearers in Dual Connectivity).

When establishing the S1 UE association, the S1AP Initial UE Message maycontain the RRC establishment cause of the first established RRCconnection. It may be possible to introduce an eNB-triggered S1APprocedure (similar to existing S1AP UE Context Modification, which todaycan only be triggered by the MME) to update the UE context in the MMEwhen the second RRC connection is established, but only if the MME wouldhave to become aware of UE context information related to having two RRCconnections (that would depend on the functional characteristics of NX,which are not yet completely defined). Otherwise, such a procedure wouldnot be needed. If the connection on the second RAT implies at least onenew radio access bearer towards the EPC, similar signaling as in LTEInitial Context Setup may have to be executed over S1.

For a UE 100 with two simultaneous RRC connections mapping towards oneS1 association towards the MME, the NW should instruct the UE 100 aboutconfiguration of signaling radio bearers (SRBs) on the respective RRCconnections. For example, how NAS PDUs should be carried once both RRCconnections are operational (the first UL NAS PDU during Attach willalways have to be carried during RRC connection establishment in thefirst RAT of course). It would be possible to either adopt duplication,to increase robustness, or to use the SRBs on the two RRC connectionsfor different purposes.

The details explained above with respect to FIGS. 1 to 6 may besummarized with respect to FIG. 7. FIG. 7 is a block diagramschematically illustrating a device embodiment of a network element 2for supporting Radio Resource Control (RRC) connection establishment ina wireless communication network.

By way of example, the network element 2 is described to implement thefunctionalities of the radio access network element 200 according to theembodiment of FIG. 1. The radio access network element 2 comprises amemory 4 and a processor 6 which may be coupled to one another. Theradio access network element may further comprise an optional interfacewhich may be coupled to the processor 6. The memory 4 contains controlinstructions executable by the processor 6. The processor 6 isconfigured to set up context information during a first RRC connectionestablishment procedure. The first RRC connection establishmentprocedure is to establish a first RRC connection towards a radio accessnetwork element of the wireless communication network implementing afirst Radio Access Technology (RAT). The context information isassociated with a wireless communication device of the wirelesscommunication network. The context information is usable for a secondRRC connection establishment procedure to establish a second RRCconnection towards a radio access network element of the wirelesscommunication network implementing a second RAT. The interface may beconfigured to carry out any communication with other components of thecommunication network. For example, the interface may transmitinformation to other components of the communication network and/or mayreceive information from other components of the communication network.

Alternatively, FIG. 7 is a block diagram schematically illustrating adevice embodiment of a network element 2 for initiating Radio ResourceControl (RRC) connection establishment in a wireless communicationnetwork.

In this case, the network element 2 is described to implement thefunctionalities of the wireless communication device 100 according tothe embodiment of FIG. 1. The radio access network element 2 comprises amemory 4 and a processor 6 which may be coupled to one another. Theradio access network element may further comprise an optional interfacewhich may be coupled to the processor 6. The memory 4 contains controlinstructions executable by the processor 6. The processor 6 isconfigured to initiating a RRC connection establishment procedure usingcontext information. The context information is associated with awireless communication device of the wireless communication network. Thecontext information is set up during a first RRC connectionestablishment procedure to establish a first RRC connection towards aradio access network element of the wireless communication networkimplementing a first Radio Access Technology (RAT). The processor 6 isconfigured to initiate, using the context information, a second RRCconnection establishment procedure to establish a second RRC connectiontowards a radio access network element of the wireless communicationnetwork implementing a second RAT. The Interface may be configured tocarry out any communication with other components of the communicationnetwork. For example, the interface may transmit information to othercomponents of the communication network and/or may receive informationfrom other components of the communication network.

FIG. 8 shows a functional block diagram of a network element 20configured in accordance with the principles of the disclosure asdescribed above. The functional blocks of the network element 20 may beimplemented by hardware, software, or a combination of hardware andsoftware to carry out the principles of the disclosure. It is understoodby a person skilled in the art that the functional blocks described inFIG. 8 may be combined into one or more blocks or separated intosub-blocks to implement the principles of the disclosure as describedabove. Therefore, the description herein may support any possiblecombination or separation or further definition of the functional blocksdescribed herein.

The radio access network element 20 of FIG. 8 is for supporting RadioResource Control (RRC) connection establishment in a wirelesscommunication network. The network element 20 comprises a set-up module22 for setting up context information during a first RRC connectionestablishment procedure. The first RRC connection establishmentprocedure is to establish a first RRC connection towards a radio accessnetwork element of the wireless communication network implementing afirst Radio Access Technology (RAT). The context information isassociated with a wireless communication device of the wirelesscommunication network. The context information is usable for a secondRRC connection establishment procedure to establish a second RRCconnection towards a radio access network element of the wirelesscommunication network implementing a second RAT.

The network element 20 may comprise a receiving module 24. The receivingmodule is for receiving, by the radio access network elementimplementing the first RAT, the context information or the informationneeded for setting up the context information.

The radio access network element implementing the first RAT correspondsto or is different from the radio access network element implementingthe second RAT.

The network element 20 may comprise a providing module 26. If the radioaccess network element implementing the first RAT is different from theradio access network element implementing the second RAT, the providingmodule is for providing, by the radio access network elementimplementing the first RAT, the context information to the radio accessnetwork element implementing the second RAT.

The providing module may further be for providing the wirelesscommunication device with information related to the establishment ofthe second RRC connection.

The providing module may further be for providing the Informationrelated to the establishment of the second RRC connection in a Downlink(DL) message of the first RRC connection establishment procedure.Alternatively, the providing module may be for providing the informationrelated to the establishment of the second RRC connection via broadcastsystem information.

The information related to the establishment of the second RRCconnection comprises at least one of: a cell identity of the cellassociated with the radio access network element implementing the secondRAT; an identifier to be used when accessing the radio access networkelement implementing the second RAT; access information for accessingthe radio access network element implementing the second RAT;information about conditions or trigger events indicating when toconnect to the radio access network element implementing the second RAT.

FIG. 9 shows a functional block diagram of a wireless communicationdevice 40 configured in accordance with the principles of the disclosureas described above. The functional blocks of the wireless communicationdevice 40 may be implemented by hardware, software, or a combination ofhardware and software to carry out the principles of the disclosure. Itis understood by a person skilled in the art that the functional blocksdescribed in FIG. 9 may be combined into one or more blocks or separatedinto sub-blocks to implement the principles of the disclosure asdescribed above. Therefore, the description herein may support anypossible combination or separation or further definition of thefunctional blocks described herein.

The wireless communication device 40 of FIG. 9 is initiating RadioResource Control (RRC) connection establishment in a wirelesscommunication network. The wireless communication device 40 comprises aninitiating module 42 for initiating, using context information, an RRCconnection establishment procedure. The context information isassociated with a wireless communication device of the wirelesscommunication network. The context information is set up during a firstRRC connection establishment procedure to establish a first RRCconnection towards a radio access network element of the wirelesscommunication network implementing a first Radio Access Technology(RAT). The initiating module is for initiating a second RRC connectionestablishment procedure to establish a second RRC connection towards aradio access network element of the wireless communication networkimplementing a second RAT.

The wireless communication device 40 may comprise a transmitting module44 for transmitting an RRC reestablishment message.

The wireless communication device 40 may comprise a providing module 46for providing the radio access network element implementing the secondRAT with a previous identifier of the wireless communication device.

As described herein, simultaneous multi-RAT connection, faster RRCconnection establishment in multi-RAT networks, lower RRC signalingload, and/or increased robustness of the RRC connection for themulti-RAT network can be facilitated by means of the devices and methodsdescribed herein.

Many advantages of the present disclosure will be fully understood fromthe foregoing description, and it will be apparent that various changesmay be made in the form, construction and arrangement of the units anddevices without departing from the scope of the present disclosureand/or without sacrificing all of its advantages. Since the presentdisclosure can be varied in many ways, it will be recognized that thepresent disclosure should be limited only by the scope of the followingclaims.

The invention claimed is:
 1. A computer program product stored in anon-transitory computer readable medium for supporting Radio ResourceControl (RRC) connection establishment in a wireless communicationnetwork, the computer program product comprising software instructionswhich, when run on one or more processors of a first radio accessnetwork element, causes the first radio access network element to: setup context information during a RRC connection establishment procedureto establish a first RRC connection between a wireless communicationdevice and the first radio access network element implementing a firstRadio Access Technology (RAT), wherein the context information isassociated with the wireless communication device of the wirelesscommunication network; and send the context information toward a secondradio access network element of the wireless communication network toestablish a second RRC connection between the wireless communicationdevice and the second radio access network element implementing a secondRAT.
 2. A computer program product stored in a non-transitory computerreadable medium for initiating Radio Resource Control (RRC) connectionestablishment in a wireless communication network, the computer programproduct comprising software instructions which, when run on one or moreprocessors of a wireless communication device, causes the wirelesscommunication device to: set up context information during a RRCconnection establishment procedure to establish a first RRC connectiontowards the first radio access network element implementing a firstRadio Access Technology (RAT), wherein the context information isassociated with the wireless communication device; receive anindication, from the first radio access network element, to set-up,using the context information, a second RRC connection between thewireless communication device and a second radio access network elementimplementing a second RAT; and responsive to the indication, set up thesecond RRC connection.
 3. A computer program product stored in anon-transitory computer readable medium for initiating Radio ResourceControl (RRC) connection establishment in a wireless communicationnetwork, the computer program product comprising software instructionswhich, when run on one or more processors of a second radio accessnetwork element, causes the second radio access network element to:receive context information from a first radio access network element ofthe wireless communication network to establish a second RRC connectionbetween the wireless communication device of the wireless communicationnetwork and the second radio access network element implementing asecond RAT, wherein the context information is associated with awireless communication device and was set up in a RRC connectionestablishment procedure to establish a first RRC connection between thewireless communication device and the first radio access networkelement; and set up the second RRC connection using the contextinformation.
 4. A first radio access network element for supportingRadio Resource Control (RRC) connection establishment in a wirelesscommunication network, the first radio access network elementcomprising: a processor; and memory containing instructions executableby the processor whereby the radio access network element is operativeto: set up context information during a first RRC connectionestablishment procedure to establish a first RRC connection between awireless communication device and the first radio access network elementimplementing a first Radio Access Technology (RAT), wherein the contextinformation is associated with the wireless communication device of thewireless communication network; and send the context information towarda second radio access network element of the wireless communicationnetwork to establish a second RRC connection between the wirelesscommunication device and the second radio access network elementimplementing a second RAT.
 5. The radio access network element of claim4, wherein the radio access network element is configured as or is partof a radio base station, a radio network controller, a NodeB, an eNodeB,or a 5G base station.
 6. A wireless communication device for initiatingRadio Resource Control (RRC) connection establishment in a wirelesscommunication network, the wireless communication device comprising: aprocessor; and memory containing instructions executable by theprocessor whereby the wireless communication device is operative to: setup context information during a RRC connection establishment procedureto establish a first RRC connection towards the first radio accessnetwork element implementing a first Radio Access Technology (RAT),wherein the context information is associated with the wirelesscommunication device; receive an indication, from the first radio accessnetwork element, to set-up, using the context information, a second RRCconnection between the wireless communication device and a second radioaccess network element implementing a second RAT; and responsive to theindication, setting up the second RRC connection.
 7. A method,implemented by a first radio access network element of a wirelesscommunication network, of supporting Radio Resource Control (RRC)connection establishment in the wireless communication network, themethod comprising: setting up context information during a RRCconnection establishment procedure to establish a first RRC connectionbetween a wireless communication device and the first radio accessnetwork element implementing a first Radio Access Technology (RAT),wherein the context information is associated with the wirelesscommunication device of the wireless communication network; and sendingthe context information toward a second radio access network element ofthe wireless communication network to establish a second RRC connectionbetween the wireless communication device and the second radio accessnetwork element implementing a second RAT.
 8. The method of claim 7,further comprising receiving, by the first radio access network elementimplementing the first RAT, the context information or informationneeded for setting up the context information.
 9. The method of claim 7,further comprising providing the wireless communication device withinformation related to the establishment of the second RRC connection.10. The method of claim 9, wherein the information related to theestablishment of the second RRC connection comprises at least one of: acell identity of the cell associated with the second radio accessnetwork element implementing the second RAT; an identifier to be usedwhen accessing the second radio access network element implementing thesecond RAT; access information for accessing the second radio accessnetwork element implementing the second RAT; and information aboutconditions or trigger events indicating when to connect to the secondradio access network element implementing the second RAT.
 11. The methodof claim 7, further comprising establishing the second RRC connectionusing the context information.
 12. The method of claim 7, furthercomprising maintaining the first RRC connection at the same time as thesecond RRC connection.
 13. The method of claim 7, further comprising, inresponse to the first RRC connection being lost, establishing the secondRRC connection.
 14. The method of claim 7, further comprisingestablishing the second RRC connection based on at least one of atrigger event and a network command.
 15. The method of claim 14, whereinthe trigger event comprises or is a Radio Link Failure (RLF) of thefirst RRC connection.
 16. The method of claim 7, wherein the first RRCconnection uses a different radio bearer than the second RRC connection.17. The method of claim 7, wherein the first radio access networkelement is a first base station; and the second radio access networkelement is a second base station different than the first base station.18. The method of claim 7, wherein the sending the context informationis in response to determining the first radio access network element isdifferent from the second radio access network element.
 19. The methodof claim 7, wherein the method further comprises sending an indicationto the wireless communication device to set up, using the contextinformation, a second RRC connection between the wireless communicationdevice and the second radio access network element.
 20. The method ofclaim 7, further comprises exchanging information with a mobilitymanagement entity regarding the second RRC connection.
 21. A method,implemented by a wireless communication device of a wirelesscommunication network, of Radio Resource Control (RRC) connectionestablishment in the wireless communication network, the methodcomprising: setting up context information during a RRC connectionestablishment procedure to establish a first RRC connection towards thefirst radio access network element implementing a first Radio AccessTechnology (RAT), wherein the context information is associated with thewireless communication device; receiving an indication, from the firstradio access network element, to set-up, using the context information,a second RRC connection between the wireless communication device and asecond radio access network element implementing a second RAT; andresponsive to the indication, setting up the second RRC connection. 22.The method of claim 21, further comprising maintaining the first RRCconnection and the second RRC connection at the same time.
 23. Themethod of claim 21, further comprising, in response to the first RRCconnection being lost, establishing the second RRC connection.
 24. Themethod of claim 21, further comprising establishing the second RRCconnection based on at least one of a trigger event and a networkcommand.
 25. The method of claim 24, wherein the trigger event comprisesor is a Radio Link Failure (RLF) of the first RRC connection.
 26. Themethod of claim 21, further comprising following setting up the secondRRC connection, reconfiguring the RRC connection to update the contextinformation for the second RRC connection.
 27. The method of claim 21,further comprising following setting up the second RRC connection,reconfiguring the RRC connection to change the bearer for the second RRCconnection.
 28. The method of claim 21, wherein the method comprisesreconfiguring the second RRC connection using anRRCConnectionReconfiguration message.
 29. A method, implemented by asecond radio access network element of a wireless communication network,of supporting Radio Resource Control (RRC) connection establishment inthe wireless communication network, the method comprising: receivingcontext information from a first radio access network element of thewireless communication network to establish a second RRC connectionbetween a wireless communication device of the wireless communicationnetwork and the second radio access network element implementing asecond RAT, wherein the context information is associated with thewireless communication device and was set up in a RRC connectionestablishment procedure to establish a first RRC connection between thewireless communication device and the first radio access networkelement; and setting up the second RRC connection using the contextinformation.
 30. The method of claim 29, wherein the first radio accessnetwork element is a first base station; and the second radio accessnetwork element is a second base station different than the first basestation.
 31. A second radio access network element for supporting RadioResource Control (RRC) connection establishment in a wirelesscommunication network, the second radio access network elementcomprising: a processor; and memory containing instructions executableby the processor whereby the radio access network element is operativeto: receive context information from a first radio access networkelement of the wireless communication network to establish a second RRCconnection between a wireless communication device of the wirelesscommunication network and the second radio access network elementimplementing a second RAT, wherein the context information is associatedwith the wireless communication device and was set up in a RRCconnection establishment procedure to establish a first RRC connectionbetween the wireless communication device and the first radio accessnetwork element; and set up the second RRC connection using the contextinformation.